Summary A continuous challenge for both single cells and multicellular organisms is that the availability of nutrients is fluctuating constantly. This is particularly the case for cancer cells in solid tumors or exposed to different stromal environments. Hence, cells must be able to sense the amount of nutrients in the environment to coordinate energy-consuming anabolic reactions with energy-producing catabolic reactions. This task is largely carried out by mTOR complex 1 (mTORC1), a protein kinase complex that senses various environmental cues and coordinates anabolic and catabolic processes to regulate cellular homeostasis. mTORC1 becomes activated when amino acids, energy sources, oxygen and growth factor levels are sufficient. Under these conditions mTORC1 promotes cell growth by boosting protein synthesis, lipid synthesis and nucleotide synthesis. However, whereas many of the key players involved in growth factor signaling to mTORC1 have been characterized, gaps remain in our understanding of how mTORC1 senses amino acids. It is also unclear how different cancer cell- associated mutations provide tumor cells with the ability to optimize usage of these regulatory components or find ways to overcome deficiencies in these mTORC1 regulators. Additionally, once activated it is still a mystery how mTORC1 regulates and coordinates the many processes required to promote cell growth, proliferation, migration, and survival, and how the altered signaling in cancer cells leads to resistance to current mTORC1 therapies with the allosteric inhibitor, rapamycin (an FDA approved mTORC1 inhibitor) and catalytic inhibitors. Furthermore, it remains unclear how mTORC1-S6K1 can regulate the variety of biological processes associated with cancer biology. To better understand mTORC1 signaling, we can now combine our mTORC1 RNAi screens, and phosphoproteome, interactome, metabolome and gene expression data sets, to support our efforts. In this proposal we have outlined several goals based on these data sets, our published work and the extensive experience of my lab, that support our long-term goals of defining mTORC1-S6K1 regulation and signaling, and for revealing new information to support efforts to kill cancer cells with activated mTORC1 signaling. Our discoveries and experience have now led us to investigate a novel mechanism for responding to amino acid deficiency (aim 1), a new pathway for regulating nuclear events linked to biological processes hijacked by cancer cells (aim 2), a novel S6K1 effector kinase, its role in mRNA biogenesis and new downstream processes (aim 3) and a new link between mTORC1-S6K1 and mRNA methylation. In conclusion, there?s a critical need for a greater understanding of the molecular basis of mTORC1 regulation and signaling, as well as its links to processes associated with cell growth, metabolism, survival and drug resistance. Our expectations are that successful completion of the proposed work will impact cancer biology/physiology and therapy through the identification of new therapeutic targets and biomarkers that can lead to the improve detection and elimination of cancer cells with unregulated mTORC1 signaling, estimated to occur in 70-80% of all human cancers.